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Kalman-filter-based undifferenced cycle slip estimation in real-time precise point positioning / Pan Li in GPS solutions, vol 23 n° 4 (October 2019)  

Public [article]  inGPS solutions > vol 23 n° 4 (October 2019) Titre : Kalman-filter-based undifferenced cycle slip estimation in real-time precise point positioning Type de document : Article/Communication Auteurs : Pan Li, Auteur ; Xinyuan Jiang, Auteur ; Xiaohong Zhang, Auteur ; et al., Auteur Année de publication : 2019 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] filtre de Kalman [Termes descripteurs IGN] glissement de cycle [Termes descripteurs IGN] interruption du signal [Termes descripteurs IGN] mesurage de phase [Termes descripteurs IGN] modèle mathématique [Termes descripteurs IGN] positionnement cinématique [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] précision du positionnement [Termes descripteurs IGN] station GLONASS [Termes descripteurs IGN] station GPS [Termes descripteurs IGN] temps réel Résumé : (Auteur) Global navigation satellite system (GNSS) precise point positioning (PPP) requires continuous carrier-phase observations to achieve a solution of high precision. Precisely correcting cycle slips caused by signal interruptions is crucial for recovering the data continuity. Most of the existing approaches usually employ only data of one epoch after the interruption for real-time cycle slip processing. In this study, we propose to introduce and estimate cycle slip parameters together with standard PPP parameters, such as position, ionospheric delay, and ambiguities in the case that possible cycle slips are detected, using a Kalman-filter-based procedure with the undifferenced and uncombined PPP model. The integer search strategy is used to fix cycle slips. To reduce the probability of wrong integer fixing, a strict integer validation threshold is suggested. As a result, it is not easy to fix all cycle slips with only one epoch of data. Our approach can be easily extended to use multi-epoch observations to enhance the cycle slip estimation. Once the cycle slips are correctly determined, continuous PPP can be achieved instantaneously. This new approach is tested and validated with three groups of experiments using GPS and GLONASS stations operated by the International GNSS Service from DOY 1–10, 2017, and a real vehicle kinematic data. Numerous experimental results showed that the proposed method can correctly fix the cycle slips for more than 99.5% of epochs suffering from re-convergence. On average, this method takes observation information from about 1.5–2.5 epochs to fix cycle slips and realize rapid re-convergence. Consequently, positioning performance is significantly improved. Numéro de notice : A2019-334 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s10291-019-0894-3 date de publication en ligne : 16/07/2019 En ligne : https://doi.org/10.1007/s10291-019-0894-3 Format de la ressource électronique : URL Article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93423 [article]

Processing of GNSS constellations and ground station networks using the raw observation approach / Sebastian Strasser in Journal of geodesy, vol 93 n°7 (July 2019)  

Public [article]  inJournal of geodesy > vol 93 n°7 (July 2019) . - pp 1045 - 1057 Titre : Processing of GNSS constellations and ground station networks using the raw observation approach Type de document : Article/Communication Auteurs : Sebastian Strasser, Auteur ; Torsten Mayer-Gürr, Auteur ; Norbert Zehentner, Auteur Année de publication : 2019 Article en page(s) : pp 1045 - 1057 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] analyse diachronique [Termes descripteurs IGN] antenne GNSS [Termes descripteurs IGN] constellation GNSS [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] erreur systématique [Termes descripteurs IGN] étalonnage d'instrument [Termes descripteurs IGN] Global Orbitography Navigation Satellite System [Termes descripteurs IGN] horloge du satellite [Termes descripteurs IGN] orbitographie [Termes descripteurs IGN] position [Termes descripteurs IGN] repère de référence [Termes descripteurs IGN] retard ionosphèrique [Termes descripteurs IGN] station GNSS [Termes descripteurs IGN] station GPS Résumé : (auteur) This article describes the raw observation approach as implemented at Graz University of Technology to determine GNSS products like satellite orbits, clocks, and station positions. To assess the performance of the approach, 15 years (2003–2017) of observations from a network of 245 globally distributed IGS stations to the GPS constellation were processed on a daily basis using the IGS14 reference frame and antenna calibrations. The resulting products are evaluated against those determined by IGS analysis centers. Orbit fit quality relative to the IGS combination is comparable to the best-fitting solutions used for evaluation. Starting from early 2017, when the IGS switched to IGS14, the determined orbits fit better to the IGS combination than any other considered solution. Midnight discontinuities show good internal orbit consistency and no noticeable satellite block-dependency. Satellite clocks are comparable to the considered IGS analysis center solutions. Station positions differ from the IGS combination on a similar level to the solutions they were evaluated against. The temporal repeatability of station positions is slightly better than that of the IGS combination. The quality of resulting GNSS products confirms that the raw observation approach is well suited for the task of determining satellite orbits, clocks, and station positions. It provides an alternative to well-established approaches used by IGS analysis centers and simplifies the introduction of additional observables from new and modernized GNSS. Numéro de notice : A2019-358 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1007/s00190-018-1223-2 date de publication en ligne : 13/12/2018 En ligne : https://doi.org/10.1007/s00190-018-1223-2 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=93426 [article]

Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model / Kibrom Ebuy Abraha in GPS solutions, vol 21 n° 1 (January 2017)  

Public [article]  inGPS solutions > vol 21 n° 1 (January 2017) . - pp 89 - 99 Titre : Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model Type de document : Article/Communication Auteurs : Kibrom Ebuy Abraha, Auteur ; Elias Lewi, Auteur ; Frédéric Masson, Auteur ; et al., Auteur Année de publication : 2017 Article en page(s) : pp 89 - 99 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes descripteurs IGN] analyse spatio-temporelle [Termes descripteurs IGN] données GPS [Termes descripteurs IGN] Ethiopie [Termes descripteurs IGN] humidité de l'air [Termes descripteurs IGN] modèle météorologique [Termes descripteurs IGN] sécheresse [Termes descripteurs IGN] station GPS [Termes descripteurs IGN] teneur en vapeur d'eau [Termes descripteurs IGN] teneur intégré en vapeur d'eau [Termes descripteurs IGN] variation saisonnière Résumé : (Auteur) We characterize the spatial–temporal variability of integrated water vapor (IWV) in Ethiopia from a network of global positioning system (GPS) stations and the European Center for Medium range Weather Forecasting (ECMWF) model. The IWV computed from the ECMWF model is integrated from the height of the GPS stations on 60 pressure levels to take both the actual earth surface and the model orography discrepancies into account. First, we compare the IWV estimated from GPS and from the model. The bias varies from site to site, and the correlation coefficients between the two datasets exceed 0.85 at different time scales. The results of this study show that the general ECMWF IWV trend is underestimation over highlands and overestimation over lowlands for wet periods, and overestimation over highlands and underestimation over lowlands for dry periods with very few exceptional stations. Second, we observe the spatial variation of the IWV. High values are obtained in those stations that are located in the north-eastern (Afar depression) sites and the south-western part of the country. This distribution is related to the spatial variability of the climate in Ethiopia. Finally, we study the seasonal cycle and inter-annual variability of IWV for all stations over Ethiopia. The main result is the strong inter-annual variability observed for the dry seasons. Numéro de notice : A2017-013 Thématique : POSITIONNEMENT Nature : Article En ligne : http://dx.doi.org/10.1007/s10291-015-0508-7 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83935 [article]

On the significance of periodic signals in noise analysis of GPS station coordinates time series / Janusz Bogusz in GPS solutions, vol 20 n° 4 (October 2016)  

Public [article]  inGPS solutions > vol 20 n° 4 (October 2016) . - pp 655 - 664 Titre : On the significance of periodic signals in noise analysis of GPS station coordinates time series Type de document : Article/Communication Auteurs : Janusz Bogusz, Auteur ; Anna Klos, Auteur Année de publication : 2016 Article en page(s) : pp 655 - 664 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Systèmes de référence et réseaux [Termes descripteurs IGN] analyse diachronique [Termes descripteurs IGN] bruit (théorie du signal) [Termes descripteurs IGN] coordonnées cartésiennes géocentriques [Termes descripteurs IGN] GIPSY-OASIS [Termes descripteurs IGN] positionnement ponctuel précis [Termes descripteurs IGN] série temporelle [Termes descripteurs IGN] signal GPS [Termes descripteurs IGN] station GPS [Termes descripteurs IGN] variation saisonnière [Termes descripteurs IGN] vitesse Résumé : (Auteur) Each of the GPS-derived time series consists of the deterministic (functional) and stochastic part. We propose that the deterministic part includes all periodicities from 1st to 9th harmonics of residual Chandler, tropical and draconitic periods and compare it with commonly used calculations of the annual and semi-annual tropical curve. Then, we address the issues of whether all residual periodicities, as proposed here, need to be taken into consideration when performing noise analysis. We use the position time series from 180 International GNSS Service stations obtained at the Jet Propulsion Laboratory using the GIPSY-OASIS software in a Precise Point Positioning mode. The longest series has 22.1 years of GPS daily solutions. The spectral indices range from –0.12 to –0.92, while the median values of “global” spectral indices are equal to: –0.41 ± 0.15, –0.38 ± 0.12 and –0.33 ± 0.18 for North, East and Up components, respectively. All non-modelled geophysical processes or non-included artificial effects in time series lead to an underestimation of errors of velocities, but also to changes in the velocity values themselves. The proposed assumption of seasonals subtraction caused the Akaike information criterion values to show a decrease in the median value of 30 %, which in fact means that all the seasonals mentioned here must be taken into account when analyzing noises. Finally, we noticed that there are some of the GPS stations that improved their velocity uncertainty even of 56 %. Numéro de notice : A2016--027 Thématique : POSITIONNEMENT Nature : Article DOI : 10.1007/s10291-015-0478-9 En ligne : http://dx.doi.org/10.1007/s10291-015-0478-9 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=83929 [article]

MIDAS robust trend estimator for accurate GPS station velocities without step detection / Geoffrey Blewitt in Journal of geophysical research : Solid Earth, vol 121 n° 3 (March 2016)    

Public [article]  inJournal of geophysical research : Solid Earth > vol 121 n° 3 (March 2016) . - pp 2054 - 2068 Titre : MIDAS robust trend estimator for accurate GPS station velocities without step detection Type de document : Article/Communication Auteurs : Geoffrey Blewitt, Auteur ; Corné Kremer, Auteur ; William C. Hammond, Auteur ; Julien Gazeaux , Auteur Année de publication : 2016 Article en page(s) : pp 2054 - 2068 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie spatiale [Termes descripteurs IGN] Amérique du nord [Termes descripteurs IGN] coordonnées GPS [Termes descripteurs IGN] estimateur [Termes descripteurs IGN] méthode robuste [Termes descripteurs IGN] série temporelle [Termes descripteurs IGN] station GPS [Termes descripteurs IGN] valeur aberrante [Termes descripteurs IGN] vitesse Résumé : (auteur) Automatic estimation of velocities from GPS coordinate time series is becoming required to cope with the exponentially increasing flood of available data, but problems detectable to the human eye are often overlooked. This motivates us to find an automatic and accurate estimator of trend that is resistant to common problems such as step discontinuities, outliers, seasonality, skewness, and heteroscedasticity. Developed here, Median Interannual Difference Adjusted for Skewness (MIDAS) is a variant of the Theil‐Sen median trend estimator, for which the ordinary version is the median of slopes vij = (xj–xi)/(tj–ti) computed between all data pairs i > j. For normally distributed data, Theil‐Sen and least squares trend estimates are statistically identical, but unlike least squares, Theil‐Sen is resistant to undetected data problems. To mitigate both seasonality and step discontinuities, MIDAS selects data pairs separated by 1 year. This condition is relaxed for time series with gaps so that all data are used. Slopes from data pairs spanning a step function produce one‐sided outliers that can bias the median. To reduce bias, MIDAS removes outliers and recomputes the median. MIDAS also computes a robust and realistic estimate of trend uncertainty. Statistical tests using GPS data in the rigid North American plate interior show ±0.23 mm/yr root‐mean‐square (RMS) accuracy in horizontal velocity. In blind tests using synthetic data, MIDAS velocities have an RMS accuracy of ±0.33 mm/yr horizontal, ±1.1 mm/yr up, with a 5th percentile range smaller than all 20 automatic estimators tested. Considering its general nature, MIDAS has the potential for broader application in the geosciences. Numéro de notice : A2016--176 Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1002/2015JB012552 date de publication en ligne : 12/02/2016 En ligne : https://doi.org/10.1002/2015JB012552 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=91799 [article]

Documents numériques

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Real time monitoring ground motion using GPS with real time corrections / R. Tu in Survey review, vol 48 n° 347 (March 2016)  

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Establishment of new Oman National Geodetic Datum ONGD14 / Y. Al-Toobi in Survey review, vol 47 n° 345 (November 2015)  

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Un évènement : 10 ans du réseau Teria / Alain Gaudet in XYZ, n° 144 (septembre - novembre 2015)

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Simulating the effects of quasar structure on parameters from geodetic VLBI / Stanislav S. Shabala in Journal of geodesy, vol 89 n° 9 (september 2015)  

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Reducing distance dependent bias in low-cost single frequency GPS network to complement dual frequency GPS stations in order to derive detailed surface deformation field / H.-Y. Chen in Survey review, vol 47 n° 340 (January 2015)  

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Precise station positions from VLBI observations to satellites: a simulation study / Lucia Plank in Journal of geodesy, vol 88 n° 7 (July 2014)  

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Determination of periodic variations in sub-daily GPS positions of volcanic areas / Gözde Akay in Geomatica [en ligne], vol 68 n° 2 (June 2014)

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Automatisation des calculs GPS des stations permanentes chiliennes / Pierre Cruchandeau (2014) 

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Non-linear station motions in epoch and multi-year reference frames / Mathis Blossfeld in Journal of geodesy, vol 88 n° 1 (January 2014)  

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Méthodes de travail dans les réseaux GNSS, 2ème partie Le positionnement statique suivant les méthodes indirectes du pivot central ou de la station virtuelle. / Romain Legros in XYZ, n° 133 (décembre 2012 - février 2013)

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